Fix cell formatting issues (#754)

* Sort text edits by descending start position

* Don't append lines to block code before formatting

* Don't apply partial edits

* Add cell-format test

* don't append newline in vdoc, fix edits out-of-range check

* Remove test

* Undo unecessary `virtualDocForCode` changes

* Add changelog entry

---------

Co-authored-by: elliot <elliot.evans@posit.co>

Author: lionel-

apps/vscode/CHANGELOG.md

@@ -5,6 +5,7 @@
 - Fixed Copilot completions in `.qmd` documents (<https://github.com/quarto-dev/quarto/pull/887>).
 - Fixed a bug where the `autoDetectColorScheme` setting could cause equation previews to have a dark text on dark background and vice versa (<https://github.com/quarto-dev/quarto/pull/864>).
 - Fix a regression where bash cell execution does not work (<https://github.com/quarto-dev/quarto/pull/826>).
+- Fix cell formatting sometimes deleting code at the end of the cell (<https://github.com/quarto-dev/quarto/pull/754>).
 
 ## 1.128.0 (Release on 2026-01-08)
 

apps/vscode/src/providers/format.ts

@@ -138,9 +138,13 @@ class FormatCellCommand implements Command {
       const edits = await formatActiveCell(editor, this.engine_);
       if (edits) {
         editor.edit((editBuilder) => {
-          edits.forEach((edit) => {
-            editBuilder.replace(edit.range, edit.newText);
-          });
+          // Sort edits by descending start position to avoid range shifting issues
+          edits
+            .slice()
+            .sort((a, b) => b.range.start.compareTo(a.range.start))
+            .forEach((edit) => {
+              editBuilder.replace(edit.range, edit.newText);
+            });
         });
       } else {
         window.showInformationMessage(
@@ -204,15 +208,20 @@ async function formatActiveCell(editor: TextEditor, engine: MarkdownEngine) {
 }
 
 async function formatBlock(doc: TextDocument, block: TokenMath | TokenCodeBlock, language: EmbeddedLanguage) {
-  const blockLines = lines(codeForExecutableLanguageBlock(block));
-  blockLines.push("");
+  // Create virtual document containing the block
+  const blockLines = lines(codeForExecutableLanguageBlock(block, false));
   const vdoc = virtualDocForCode(blockLines, language);
+
   const edits = await executeFormatDocumentProvider(
     vdoc,
     doc,
     formattingOptions(doc.uri, vdoc.language)
   );
+
   if (edits) {
+    // Because we format with the block code copied in an empty virtual
+    // document, we need to adjust the ranges to match the edits to the block
+    // cell in the original file.
     const blockRange = new Range(
       new Position(block.range.start.line, block.range.start.character),
       new Position(block.range.end.line, block.range.end.character)
@@ -224,8 +233,17 @@ async function formatBlock(doc: TextDocument, block: TokenMath | TokenCodeBlock,
           new Position(edit.range.end.line + block.range.start.line + 1, edit.range.end.character)
         );
         return new TextEdit(range, edit.newText);
-      })
-      .filter(edit => blockRange.contains(edit.range));
+      });
+
+    // Bail if any edit is out of range. We used to filter these edits out but
+    // this could bork the cell.
+    if (adjustedEdits.some(edit => !blockRange.contains(edit.range))) {
+      window.showInformationMessage(
+        "Formatting edits were out of range and could not be applied to the code cell."
+      );
+      return [];
+    }
+
     return adjustedEdits;
   }
 }

packages/quarto-core/src/markdown/language.ts

@@ -38,11 +38,14 @@ export function isExecutableLanguageBlock(token: Token) : token is TokenMath | T
   }
 }
 
-export function codeForExecutableLanguageBlock(token: TokenMath | TokenCodeBlock) {
+export function codeForExecutableLanguageBlock(
+  token: TokenMath | TokenCodeBlock,
+  appendNewline = true,
+) {
   if (isMath(token)) {
     return token.data.text;
   } else if (isCodeBlock(token)) {
-    return token.data + "\n";
+    return token.data + (appendNewline ? "\n" : "");
   } else {
     return "";
   }